Modeling ice shelf cavities in a z coordinate ocean general circulation model

Abstract. Processes at the ice shelf-ocean interface and in particular in ice shelf cavities around Antarctica have an observable effect on the solutions of basin scale to global coupled ice-ocean models. Despite this, these processes are not routinely represented in global ocean and cli-mate models. It is shown that a new ice shelf cavity model for z-coordinate models can re-produce results from an intercomparison project of earlier approaches with vertical σ- or isopy-cnic coordinates. As a proof of concept, ice shelves are incorporated in a 100 year global in-tegration of a z-coordinate model. In this simulation, glacial melt water can be traced as far as north as 15 ◦ S. The observed effects of processes in the ice shelf cavities agree with pre-vious results from a σ-coordinate model, notably the increase in sea ice thickness. However, melt rates are overestimated probably because the parameterization of basal melting does not suit the low resolution of this configuration. 1

Prévention des crises en Afrique subsaharienne. Relever le défi de l'emploi : l'agriculture au centre

En Afrique subsaharienne, 330 millions de jeunes arriveront sur le marché du travail dans les quinze prochaines années. C'est la population actuelle des États-Unis. Cet afflux peut être porteur de développemen, sous réserve d'une croissance créatrice d'emplois. Sinon, des risques politiques majeurs sont à craindre pour l'Afrique et le reste du monde. Or les économies africaines restent majoritairement agricoles et la compétition internationale laisse peu de marges de manoeuvre pour une diversification économique rapide. Des emplois devront donc être créés massivement dans l'agriculture et le secteur rural, d'autant qu'environ 200 millions des nouveaux actifs vivront en zone rurale. Pour relever ce défi, et aussi celui de la sécurité alimentaire, il est urgent d'établir des priorités d'action dont l'objectif est de toucher le plus grand nombre. Il s'agit dès lors de privilégier les agricultures familiales, d'appuyer le développement des filières de produits vivriers, et d'accélérer la diversification rurale en renforçant les économies locales de façon durable

Unsupervised Multi Class Segmentation of 3D Images with Intensity Inhomogeneities

Intensity inhomogeneities in images constitute a considerable challenge in image segmentation. In this paper we propose a novel biconvex variational model to tackle this task. We combine a total variation approach for multi class segmentation with a multiplicative model to handle the inhomogeneities. Our method assumes that the image intensity is the product of a smoothly varying part and a component which resembles important image structures such as edges. Therefore, we penalize in addition to the total variation of the label assignment matrix a quadratic difference term to cope with the smoothly varying factor. A critical point of our biconvex functional is computed by a modified proximal alternating linearized minimization method (PALM). We show that the assumptions for the convergence of the algorithm are fulfilled by our model. Various numerical examples demonstrate the very good performance of our method. Particular attention is paid to the segmentation of 3D FIB tomographical images which was indeed the motivation of our work

Estimating Oceanic Export Production based on 3D coupled physical-biogeochemical modelling

The study addresses various aspects of model-based estimating the oceanic primary production. In particular, we consider existent interpretations of the export fluxes; influence of implied conversions between modelled chlorophyll and biomass, expressed in nitrogen and/or carbon units, and, therefore, impact of decoupling the biogeochemical (N, C) cycles and chlorophyll. The export production is estimated by simulating global ocean biolgeochemical dynamics with the CN regulated model (REcoM) developed by Schartau et al. (2007) and coupled with the MITgcm. The model describes carbon (C) and nitrogen (N) fluxes between components of the ocean ecosystem. The nitrogen and carbon cycles as well as phytoplankton chlorophyll (Chl) dynamics are decoupled in accordance with the dynamic regulatory phytoplanktonic acclimation model sugested by Geider et al. (1998). Sensitivity of the primary production estimates to biological model parameters is also discussed